Hi China
I reckon you might need a couple of days, depending on how many surnames you're researching.
In addition to all the photos, there are hand-written family trees, volumes full of press cuttings on microfilm plus the correspondence of the Gypsiologists which often includes notes on British Gypsy families. Last time I was there, they had a computerised name index to press cuttings and correspondence in the search room but you'll need to check that this is still available.
There's also a full run of the Journal of the Gypsy Lore Society (starting from 1888) which contains many articles about British Gypsy families. Unfortunately, there isn't (yet) a master name index to the JGLS. But each annual volume is name indexed.
Best wishes
Sharon